The present invention relates to power assist modules for use in roller shades. A spring is typically used to assist in raising (retracting) a roller shade. Typically, depending on the width and weight of the roller shade, the spring used to assist in raising the shade is custom supplied for each application.
In a top down roller shade, the entire light blocking material typically wraps around a rotator rail (also referred to as a rotator tube or roller tube) as the shade is raised (retracted). Therefore, the weight of the shade is transferred to the rotator rail as the shade is raised, and the force required to raise the shade is thus progressively lower as the shade (the light blocking element) approaches the fully raised (fully open or retracted) position. Of course, there are also bottom up shades and composite shades which are able to do both, to go top down and/or bottom up. In the case of a bottom/up shade, the weight of the shade is transferred to the rotator rail as the shade is lowered, mimicking the weight operating pattern of a top/down blind.
A wide variety of drive mechanisms is known for extending and retracting coverings—moving the coverings vertically or horizontally or tilting slats. A number of these drive mechanisms may use a spring motor to provide the catalyst force (and/or to supplement the operator supplied catalyst force) to move the coverings. Typically, in order to finely counterbalance the weight of a roller shade to make it easier to raise the shade when using some of these control mechanisms, a different spring is supplied for each incremental change in shade width and/or in shade material. Not only does the length of the spring change, but also the K value (the spring constant) changes. This means that the supplier ends up carrying a large inventory of springs in order to cover all the combinations of roller shades which may be sold.
It is also desirable to be able to provide a “pre-wind” on the spring to ensure that the spring provides assistance in retracting the shade all the way to the fully retracted position of the shade.
Prior art roller shades, such as the shade described in WO 2008/141389 “Di Stefano” published Nov. 27, 2008, which is hereby incorporated herein by reference, provide booster assemblies 100, 102 (See FIG. 1), either mounted on a common shaft or on different portions 104, 106 of a common shaft, which are interconnected by connecting pieces 122 (See FIG. 2) or 208 (See FIG. 5). As a result, it would be extremely awkward and difficult to provide a “pre-wind” to each booster assembly, particularly if it is desired to provide a different degree of “pre-wind” to each booster assembly. In fact, Di Stefano does not disclose any mechanism or procedure to allow any “pre-wind” to be added to the booster assemblies.
In any event, to the extent that some degree of “pre-wind” could be added to prior art booster assemblies, the degree of “pre-wind” would be maintained by the interaction between the roller tube and the fixed shaft. As soon as the shaft is removed from inside the roller tube (or alternatively, as soon as the roller tube is removed from outside the shaft), any degree of “pre-wind” of the booster assemblies would be lost.